To make dentures in the dentistry, first, a master mold has to be made according to the teeth profile of the patient, then a denture is formed based on the master mold. The process of making the master mold includes mixing a molding powder or gypsum with water evenly to become viscous and curing the mixed material to become a desired shape.
The mixing operation can be accomplished through a mixer such as the one disclosed in R.O.C. patent publication No. 274741 entitled “Molding material mixer”. It has a transmission mechanism with a planetary gear. When a motor in the mixer is activated, a holding trough and a holding cup pivotally located on a V-shaped chassis are rotated in opposite directions to mix the molding material.
FIG. 1 shows another “Improved transmission structure for mixers of dental molding powder” disclosed in R.O.C. patent No. M278473 that was submitted by the Applicant. It includes two belts and a plurality of pulleys and a pressing means. The pulleys are mounted onto a V-shaped chassis which has a holding trough and a holding cup located in the holding trough. The V-shaped chassis is mounted onto a spindle of a motor. The two belts wind on the pulleys. One of the belts also winds on the holding cup. When the motor is activated, the spindle of the motor drives the V-shape chassis rotating. Through chain movements of the belts and pulleys, the holding trough and holding cup on the V-shaped chassis rotate. When the mixer is rotated and used for a period of time, fatigue often occurs to the belts. The operation of the mixer is affected. Hence the belts have to be replaced regularly to maintain a desired operating condition. But the dimension of the belts is designed according to the specifications of the entire transmission mechanism. To remove the belts from the V-shaped chassis is difficult. And the holding trough and other elements have to be removed from the V-shaped chassis to do belt replacement. As shown in FIG. 1, the pulleys are located below the V-shaped chassis, and the belts are coupled on the spindle and pressed below the holding trough and the V-shaped chassis. Hence replacing the belts on the transmission structure is difficult and time-consuming.